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Original Research
Are Bonding Agents being Effective on the Shear Bond Strength of
Orthodontic Brackets Bonded to the Composite?
Fahimeh Farzanegan1, Behrad Tanbakuchi2
1
Dental Research Center, Department of Orthodontics, Faculty of Dentistry, Mashhad University of
Medical Sciences, Mashhad, Iran
2
Department of Orthodontics, Mashhad University of Medical Sciences, Mashhad, Iran
Received 8 July 2013 and Accepted 7 December 2013
Abstract
Introduction: One of the clinical problems in
orthodontics is the bonding of brackets to composite
restorations. The aim of this study was to evaluate the
shear bond strength of brackets bonded to composite
restorations using Excite. Methods: Forty brackets were
bonded to composite surfaces, which were embedded in
acrylic resin. One of the following four protocols was
employed for surface preparation of the composite:
group 1) 37% phosphoric acid for 60 seconds, group 2)
roughening with a diamond bur plus 37% phosphoric
acid for 60 seconds, group 3) 37% phosphoric acid for
60 seconds and the applying Excite®, group 4)
roughening with diamond bur plus 37% phosphoric acid
for 60 seconds and applying Excite®. Maxillary central
brackets were bonded onto the composite prepared
samples with Transbond XT. Shear Bond Strength
(SBS) was measured by a universal testing machine.
The ANOVA and Tukey test was utilized for data
analysis. Results: There was a significant difference
between the four groups (P<.000). The lowest and
highest SBS were attributed to the Group 1 and Group 4
respectively. There was no significant difference
between Groups 1 & 3, 2 & 3 and 2 & 4. However,
differences between Group 1 in comparison with
Groups 2 and 4 and Group 3 with Group 4 were
statistically significant. Conclusion: According to the
results of this study, the usage of Excite® alone before
bonding brackets to composite restorations does not
cause an increase in bond strength. However,
roughening the composite surface before applying
Excite is very effective for improving the bond strength
of orthodontic brackets to composite restorations.
Keywords: Bond strength, composite restorations,
orthodontic brackets.
Farzanegan and Tanbakuchi
--------------------------------------------------------Farzanegan F, Tanbakuchi B. Are Bonding Agents being
Effective on the Shear Bond Strength of Orthodontic Brackets
Bonded to the Composite?. J Dent Mater Tech 2014; 3(2):
61-5.
Introduction
Today, adults compose a significant number of
orthodontic patients. Therefore, bonding orthodontic
brackets to composite restorations is becoming an
increasingly common procedure in the daily practice of
orthodontics (1-6). Many studies have shown when the
aged composite restorations have been polished,
contaminated or laboratory processed, the bond strength
of them to the new composite restorations is
significantly reduced (4,6-11). In order to maximize the
bond strength between the two composite restorations, a
number of techniques have been suggested in literature
such as acid etching, micro etching and the use of
chemical agents (12-14).
In restorative dentistry, a number of studies have
focused on repairing the composite resin. These studies
have demonstrated that the use of intermediate bonding
agents e.g. adhesive or saline and roughening the
surface of the old composites significantly improve the
adhesion of the new composite restorations (15-19).
Unlike restorative dentistry, in orthodontics, a durable
bond is not intended.
Rather, optimal adhesion to the surface of the
composite restoration is sought which allow for
orthodontic treatment without bond failure (13). It has
been suggested that bond strengths of 6–10 MPa are
sufficient for orthodontic objectives (20).
Although brackets bonded to the freshly roughened
surface of an old composite restoration have had clinical
JDMT, Volume 3, Number 2, June 2014
61
success, some authors recommend an intermediate
primer as well (21).
Excite (Ivoclar.Vivadent, Schaan, Liechtenstein) is a
fifth-generation, light-activated dentin bonding agent
that sometimes called one bottle system. It is
recommended for direct bonding of resin composite,
Ceromer™, and compomers to enamel and dentin. This
type of adhesive combines the primer and bonding agant
into a single solution and is acetone-free. A separate
etching step still is required (22).
According to the manufacturer, Excite is
distinguished from other "one-component" bonding
agents in that it contains extremely small (i.e., 12nanometer) filler particles. Because they are so small,
the manufacturer claims that the filler particles can
penetrate into the demineralized dentin and contribute to
formation of the hybrid layer. Another reported
advantage of their small size is that they do not
contribute significantly to the adhesive's film thickness.
Few studies in orthodontic fields have been
published in literature on this subject, none of which
have investigated the usage of Excite as bonding agent.
Consequently, the present study was undertaken with
the aim of assessing the bond strength of bonded
brackets to composite restorations that were subjected to
different surface treatments, including the usage of
Excite.
Materials and Methods
Forty cylindrical acrylic blocks, with a diameter of
8mm and a length of 16mm, were employed in this
study. After complete polymerization with cold cured
acryl (Acropars, Tehran, Iran), a retentive cavity, with
the dimensions of 6×6×1.5mm, was prepared in each
block by a fissure diamond bur (Schoufa, Japan). The
opposite walls of this cavity were convergent to increase
mechanical retention. This cavity was then filled with
anterior dental composite (3M ESPE, Minnesota, USA)
with the shade of A2. By a manual instrument the
surface of the dental composite was carefully flattened.
Afterward, the layer of composite was cured by a light
cure unit (Bluephase-C8, Leichtenstein) for 20 seconds.
The specimens were randomly divided into four groups
of 10.
In the first group, the surface of the composite was
etched with 37% phosphoric acid (Ultra Etch, UltraDent, USA) for 60 seconds. Then, the maxillary central
brackets (Dentarum Dental Technology, Ispringen,
Germany) were bonded using Transbond XT (3M,
ESPE, Minnesota, USA) according to the
manufacturer’s instructions. After positioning the
brackets, the excess composite was removed with a
scaler and the composite light cured mesially, distally,
62 JDMT, Volume 3, Number 2, June 2014
occlusally and gingivally for 5 seconds for each side,
according to manufacturer guideline.
In the second group, after roughening the surface of
the composite with a diamond bur (Schoufa, Japan),
phosphoric acid was applied to the surface of the
composite and the brackets were bonded in a same
manner as group 1.
In the third group, after using phosphoric acid and
rinsing,
Excite
(Ivoclar,
Vivadent,
Schaan,
Leichtenstein) was applied by a microbrush on the
surface of the composites. After light curing of the
Excite for 20 seconds, the brackets were bonded similar
to group 1.
In the fourth group, the specimens were initially
roughened with a diamond bur and then the phosphoric
acid was applied to the surfaces. After rubbing in the
Excite and curing it, the brackets were bonded just like
the previous groups.
The specimens were then stored in an incubator
(Thelco, GCA, England) for 24 hours at 37˚C and 100%
humidity. Shear bond testing was performed using a
universal testing machine (Zwick, Germany) at a
crosshead speed of 0.5 mm/minute and a 200 kg load
cell 23. The shear force was applied vertically across the
bracket and the composite interface. The force required
to shear the brackets was recorded in Newton
measurements. The bond strengths were calculated in
megapascals (MPa) by dividing the force to the surface
of the base of the brackets (2mm).The results were
statistically analyzed using one-way ANOVA and
Tukey. The level of significance for all tests was
determined at P<0.05.
Results
The normal distribution of data was confirmed by
the Kolmogorov-Smirnov test. The descriptive data of
the shear bond strength of the different groups is shown
in Table 1.The highest bond strength was that of Group
4, which used roughening and bonding in addition to
acid. Group 1 had the lowest bond strength which used
only acid etch technique before bonding the bracket. In
addition Table 1 presents the ANOVA results.
According to this analysis, there was a significant
difference in the shear bond strength of the different
groups (P<0.001).
The results of the Tukey test are given in Table 2.
This test indicated that there were significant
differences between the shear bond strength of groups 1
and 2 (P=0.007), groups 1 and 4 (P=0.001) and that of
group 3 when compared with Group 4 (P=0.015).
However, the differences of shear bond strength of
Groups 1 and 3, Groups 2 and 3 and Groups 2 and 4 was
not statistically significant.
Bonding Agents
Table 1. Descriptive statistics of shear bond strength of different groups and ANOVA result
Group
N
Mean
Sd. Deviation
Sd. Error
P-Value
1
10
5.8315
3.11189
.98407
<0.001
2
10
11.3697
3.81686
1.20700
3
10
8.9593
3.38463
1.07031
4
10
13.7543
3.17005
1.00246
Total
40
9.9787
4.40309
.69619
(group 1: acid, group 2: acid+roughing, group 3: acid+bonding, group 4: acid+roughing+bonding)
‫٭‬The mean difference is significant at the .05 level
Table 2. Tukey test results of shear bond strength differences of four study groups
Group
N
Subset for alpha = .05
1
2
3
1
10
5.8315
3
10
8.9593
8.9593
2
10
11.3697
11.3697
4
10
13.7543
Sig.
.183
.395
.404
(group 1: acid, group 2: acid+roughing, group 3: acid+bonding, group 4: acid+roughing+bonding)
Discussion
Clinical studies that assess the shear bond strength
of orthodontic brackets are extremely difficult to
conduct. It is virtually impossible to standardize the oral
status of each patient, which hinders the prediction of
durability and the comparison of dental materials 24.
Thus, laboratory methods have been proposed to
simulate oral conditions and facilitate comparisons
among different dental materials.
In order to improve the bond strength of new
composite restorations to previous composite fillings,
various techniques have been presented such as acid
etching, micro etching and the use of chemical agents in
restorative dentistry (12-14).
This study used four protocols for preparing the
composite surface before the bonding of brackets,
including the application of phosphoric acid, the
creation of roughness, the rubbing of Excite, and a
combination of these methods.
As recommended by numerous researchers,
roughening the bonded surface results in increased bond
strength (25). Similarly, the results of the present study
also suggest that roughening the surface of composite
restorations enhances bond strength. The findings of
Chay et al. (26) support the claim that treatment, such as
roughening with greenstone or sandblasting the surface
of the provisional material, produced increased bond
strength of orthodontic brackets after artificial aging.
Farzanegan and Tanbakuchi
A previous study (23) found that, when stainless
steel brackets are bonded to composite restorations,
treated with diamond bur there is significant higher
shear bond strength than those, bonded to composite
surfaces treated with hydrofluoric acid. Those results
are similar to the current study, except that phosphoric
acid was used in the latter instead of hydrofluoric acid.
Germec et al concluded that air abrasion leads to
more improved retentive surfaces than roughening with
a diamond bur when bonding brackets to amalgam (25).
Although no previous study has investigated the effect
of a bonding agent, such as Excite on the shear bond
strength of orthodontic brackets bonded to a composite,
the most similar study to date was performed by
Eslamian (27). Eslamian et al reported that using a
silane agent offered no advantage when bonding
orthodontic brackets to composite restorations (27).
Their study supports the current study's findings that the
usage of an intermediate agent alone, such as Excite,
has no effect on shear bond strength.
In the present study, however, the strongest bond
strength was achieved with the application of Excite in
addition to roughening and acid etching on the
composite surface. The role of Excite in bond
strengthening is attributed to its capability of improving
surface wetting. Excite, as a bonding agent, by
enhancing the wetting of composite restoration surfaces
can lead to the formation of more resin tags. Increasing
JDMT, Volume 3, Number 2, June 2014
63
the number of resin tags boosts the shear bond strength
of brackets to composite restorations. It seems that
roughening the composite surface provides conditions
for Excite to form more resin tags and so augment bond
strength.
bond strength and clinical techniques. J Prosthet D
1989;61:669-75.
11. Crumpler DC, Bayne SC, Sockwell S, Brunson D,
Roberson TM. Bonding to resurfaced posterior
composites. Dent Mater 1989;5:417-24.
Conclusion
12. Livaditis GJ, Thompson VP. Etched castings: an
According to the results of this study, the usage of
Excite® alone before the bonding of brackets to
composite restorations does not cause an increase in
bond strength. However, roughening the composite
surface is very effective in improving of the bond
strength of orthodontic brackets bonded to composite
restorations, especially before the application of Excite.
improved retentive mechanism for resin-bonded
retainers. J Prosthet Dent 1982;47:52-8.
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bonding of orthodontic
brackets to
esthetic
restorative materials using a silane. Am J Orthod
Dentofacial Orthop1984;86:503-6.
14. Livaditis GJ. A chemical etching system for
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Corresponding Author:
Behrad Tanbakuchi
Dental Research Center
Vakilabad Blvd, Mashhad, Iran
Tel: 0985118829501
Fax: 00985118829500
E-mail: [email protected]
Farzanegan and Tanbakuchi
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65